linux-kernel - Re: [PATCH] watchdog: mtk_wdt: Move mt6589-wdt fallback compatible to end of list

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Message-ID: <CAGXv+5EHYJBTvXxB-HdqVDzSNU7bqHRSBxKfonVm_p5jjYyMSQ@mail.gmail.com>
Date:   Mon, 1 Aug 2022 17:31:53 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] watchdog: mtk_wdt: Move mt6589-wdt fallback compatible to
 end of list

On Tue, Jul 26, 2022 at 9:25 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 7/26/22 01:37, AngeloGioacchino Del Regno wrote:
> > Il 26/07/22 08:20, Chen-Yu Tsai ha scritto:
> >> The watchdog facility in the MediaTek SoCs are all the same, but the
> >> hardware block also contains a reset controller, which differs in the
> >> number of resets used between different SoCs. This difference is
> >> supported with of_device_get_match_data() supplying the number of reset
> >> lines for the newer compatible strings. The original mt6589-wdt only
> >> covers the watchdog facility.
> >>
> >> of_device_is_compatible(), and by extension of_device_get_match_data(),
> >> works by going through the given list of compatible strings sequentially,
> >> and checks if any of the device node's compatible strings match.
> >>
> >> To avoid early matching on the "mediatek,mt6589-wdt" fallback compatible,
> >> which only provides watchdog functionality and no reset controller, move
> >> the fallback entry to the end of the list, so that other, more specific
> >> compatible strings have a chance at getting matched.
> >>
> >> Fixes: c254e103082b ("watchdog: mtk_wdt: mt8183: Add reset controller")
> >> Fixes: adc318a34066 ("watchdog: mt8192: add wdt support")
> >> Fixes: 8c6b5ea6ac68 ("watchdog: mediatek: mt8195: add wdt support")
> >> Fixes: 4dbabc4d9e8c ("watchdog: mediatek: mt8186: add wdt support")
> >> Fixes: 711a5b25bac9 ("watchdog: mtk_wdt: mt7986: Add toprgu reset controller support")
> >> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
> >
> > Uhm, I don't think that this is an issue?
> >
> > Ordering precedence is given to the list that you specify in devicetree, that's why
> > "the second one" is a fallback, meaning: ("impossible" example below)
> >
> > compatible = "mediatek,mt8195-wdt", "mediatek,mt8183-wdt", "mediatek,mt6589-wdt";
> >
> > This gets walked as per the order in which you wrote the compatibles, so:
> > * Check match for mt8195-wdt, does not exist?
> >   * Check match for mt8183-wdt, exists!
> >   * Put everything into dev->of_node (having mediatek,mt8183-wdt only!)
> >
> > __of_device_is_compatible() gets dev->of_node and compares that to all of the
> > possible matches.
> >
> > struct device_node for this device hence does *not* contain any of the other
> > compatibles that we specified in devicetree, so it does *not* contain any of
> > "mediatek,mt8195-wdt", or "mediatek,mt6589-wdt", because we have previously
> > successfully matches 8183.
> >
> > I don't think that I've misinterpreted this flow, but if I have, let's pull
> > in devicetree people and check with them?
> >
>
> I don't see the problem either. The fallback needs to be listed last in the
> compatible property. If it isn't, having it last in struct of_device_id
> won't help either.

I was probably reading something that wasn't there in the watchdog patch
series I mentioned. I've replied over there. Please ignore this one for
now.

ChenYu

> > Cheers,
> > Angelo
> >
> >> ---
> >>
> >> This change complements the removal of the fallback compatible from the
> >> bindings and DTSI files [1].
> >>
>
> If the fallback isn't listed in the dtsi files, it won't match at all,
> no matter where it is located in struct of_device_id.
>
> Guenter
>
> >> [1] https://lore.kernel.org/linux-mediatek/20220721014845.19044-1-allen-kh.cheng@mediatek.com/
> >>
> >>   drivers/watchdog/mtk_wdt.c | 3 ++-
> >>   1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/watchdog/mtk_wdt.c b/drivers/watchdog/mtk_wdt.c
> >> index e97787536792..3d5a239b93ba 100644
> >> --- a/drivers/watchdog/mtk_wdt.c
> >> +++ b/drivers/watchdog/mtk_wdt.c
> >> @@ -425,12 +425,13 @@ static int mtk_wdt_resume(struct device *dev)
> >>   static const struct of_device_id mtk_wdt_dt_ids[] = {
> >>       { .compatible = "mediatek,mt2712-wdt", .data = &mt2712_data },
> >> -    { .compatible = "mediatek,mt6589-wdt" },
> >>       { .compatible = "mediatek,mt7986-wdt", .data = &mt7986_data },
> >>       { .compatible = "mediatek,mt8183-wdt", .data = &mt8183_data },
> >>       { .compatible = "mediatek,mt8186-wdt", .data = &mt8186_data },
> >>       { .compatible = "mediatek,mt8192-wdt", .data = &mt8192_data },
> >>       { .compatible = "mediatek,mt8195-wdt", .data = &mt8195_data },
> >> +    /* Fallback compatible string must be last entry */
> >> +    { .compatible = "mediatek,mt6589-wdt" },
> >>       { /* sentinel */ }
> >>   };
> >>   MODULE_DEVICE_TABLE(of, mtk_wdt_dt_ids);
> >
> >
>